1. Field
The following description relates to remotely monitoring and controlling electrical motors in oil and gas well stimulation hydraulic fracturing applications. For example, an apparatus and method allows an operator to remotely monitor and control, through wired connections and/or wirelessly, one or more alternating current motors in oil and gas well stimulation hydraulic fracturing applications.
2. Description of Related Art
Hydraulic fracturing is the process of injecting treatment fluids at high pressures into existing oil or gas wells in order to stimulate oil or gas production. The process involves the high-pressure injection of “fracking fluid” (primarily water, containing sand or other proppants suspended with the aid of thickening agents) into a wellbore to create cracks in the deep-rock formations through which natural gas, petroleum, and brine will flow more freely. When the hydraulic pressure is removed from the well, small grains of hydraulic fracturing proppants (such as sand or aluminum oxide) hold the fractures open. A typical stimulation treatment often requires several high pressure fracturing pumps operating simultaneously to meet pumping rate requirements.
Hydraulic-fracturing equipment typically consists of one or more slurry blender units, one or more chemical hydration units, one or more fracturing pump units (powerful triplex or quintuplex pumps) and a monitoring unit. Associated equipment includes fracturing tanks, one or more units for storage and handling of proppant and/or chemical additives, and a variety of gauges and meters monitoring flow rate, fluid density, and treating pressure. Fracturing equipment operates over a range of pressures and injection rates, and can reach 100 megapascals (15,000 psi) and 265 litres per second (9.4 cu ft/s) (100 barrels per minute).
Hydraulic fracture treatment can be monitored by measuring the pressure and rate during the formation of a hydraulic fracture, with knowledge of fluid properties and proppant being injected into the well. This data, along with knowledge of the underground geology can be used to model information such as length, width and conductivity of a propped fracture. By monitoring the temperature and other parameters of the well, engineers can determine collection rates, and how much fracking fluid different parts of the well use.
Diesel engines have been used as the primary driving mechanism for fracturing pumps in the past. Using diesel engines, however, has serious disadvantages, including the relative inefficiency of the internal combustion engine and the fact that its operation is costly. In addition, off-road diesel engines of the types used for hydraulic fracturing are noisy while pumping, limiting the areas in which they may be used. Also, diesel engines have many moving parts and require continuous monitoring, maintenance, and diagnostics. Ancillary subsystems are typically driven hydraulically in traditional diesel-driven systems, which also contribute to other operational problems.
In view of the above deficiencies, electrical motors for hydraulic fracturing operations potentially offer an attractive alternative. Electrical motors are lighter, have fewer moving parts, and can more easily be transported. Further, the control of electrical motors provides many advantages over traditional diesel-driven, variable gear ratio powertrains, for example, through more precise, continuous speed control. During operation, electrical motors may be controlled with specific speed settings and can be incremented or decremented in single RPM (revolutions per minute) intervals without interruption. Also, automatic control operations can allow for the most efficient distribution of power throughout the entire system. The use of electrical motors obviates the need for supplying diesel fuel to more traditional fracturing pumps, and reduces the footprint of the site, and its environmental impact. Other advantages of electrical motors include, but are not limited to, the ability to independently control and operate ancillary sub systems.
Electrical motors are available in two main varieties, dependent on the methods of voltage flow for transmitting electrical energy: direct current (DC) and alternating current (AC). With DC current, the current flow is constant and always in the same direction, whereas with AC current the flow is multi-directional and variable. The selection and utilization of AC motors offers lower cost operation for higher power applications. In addition, AC motors are generally smaller, lighter, more commonly available, and less expensive than equivalent DC motors. AC motors require virtually no maintenance and are preferred for applications where reliability is critical.
Additionally, AC motors are better suited for applications where the operating environment may be wet, corrosive or explosive. AC motors are better suited for applications where the load varies greatly and light loads may be encountered for prolonged periods. DC motor commutators and brushes may wear rapidly under this condition. VFD drive technology used with AC motors has advanced significantly in recent times to become more compact, reliable and cost-effective. DC drives had a cost advantage for a number of years, but that has changed with the development of new power electronics like IGBT's (Insulated-gate bipolar transistors).
Despite the potential advantages associated with electrical motors of both types, and the continuing need for improvement, the use and control of hydraulic fracturing operations using electrical motors has not been successfully implemented in practice.